The present invention relates to hydraulic systems, and more particularly to a hydraulic system for an auxiliary load transfer device connected to the rear of a truck.
Auxiliary load transfer devices for trucks generally include an axle with a pair of wheels thereon pivotally mounted to the rear of a truck such as a concrete mixing truck. The auxiliary load transfer device is employed to relieve the conventional rear wheels of the truck of some of the truck weight and to transfer some of the truck weight from the rear wheels to the truck's front wheels. In order to accomplish this, a hydraulic cylinder is interposed between the truck and the load transfer device and is operable through a hydraulic circuit to raise the auxiliary axle when not in use or to lower the auxiliary axle and provide selected support of the rear of the truck. An example of an auxiliary load transfer device and the hydraulic circuitry therefore can be found in U.S. Pat. No. 4,084,833.
It has been found that when the auxiliary load transfer device is in use and the truck is driven up an incline or over a bumpy road so that the wheels of the auxiliary device drop below the rear wheels of the truck, the truck driver may feel a weaving or wandering of the rear of the truck. This weaving or wandering may occur because the pressure in the main hydraulic line leading to the hydraulic cylinder gradually increases each time the wheels of the auxiliary axle drop below the rear wheels of the truck since the pump automatically increases its output pressure each time this occurs. As a result, more pressure is applied against the load transfer device than is desired. This transfers too much of the truck weight to the truck's front wheels thus resulting in a feeling of weaving or wandering of the truck during travel.
It is therefore an object of the present invention to provide a means for preventing the build-up of excess pressure in the main hydraulic line between the pump and hydraulic cylinder so as to prevent weaving or wandering of the rear of the truck.